Super-automatic coffee machines are known in the art.
Super-automatic machines conventionally comprise machines in which it is provided that dosage of ground coffee and supply of coffee are controlled by the machine, whereby the latter may be activated by an operator or a user.
Super-automatic machines comprise, in general, a brewing assembly comprising an infusion chamber consisting of a brewing cylinder and two pistons, namely an upper piston or closing member and a lower piston.
In several working steps, the machine takes ground coffee, brews the coffee generating a brick of exhausted coffee powder and ejects the coffee brick. Then one of the pistons or both move(s) back to their resting position(s).
In its resting position the upper piston, in general, is not in the brewing cylinder and in some cases is not mobile; the lower piston moves by remaining inside the brewing cylinder both during the working steps and in its resting position.
According to the known art, each piston comprises one or more gaskets or sealing elements made of different materials. The upper piston comprises for instance at least one Turcon® gasket of known type and the lower piston comprises at least one silicone gasket.
A known problem, especially as far as the lower piston is concerned, is that the gasket or gaskets is or are not able to prevent leaks, that is to impede that some drops of liquid or water pass through the gasket(s): actually, on the one side, the sealing elements on the closing member and the lower piston are subjected to a strong thermal stress due to the high temperatures in the infusion chamber whereas, on the other side, especially the sealing element of the lower piston is exposed to an additional mechanical stress due to the piston movement relative to the cylinder.
Moreover, finely ground coffee powder, with a flour-like consistency, adheres to the inner wall of the cylinder of the infusion chamber and is tamped against the sealing element because of the pressure or over-pressure existing in the chamber, for instance 9-10 bars. While the piston(s) is (are) moving, such a mixture of hot water and coffee powder acts as an abrasive and this, jointly with the thermal stress, causes the sealing element(s) to become fragile or degraded, whereby the piston moves with difficulty and eventually it is no longer tightly guided in the cylinder.
In summary, for all the above reasons, leaks can frequently occur and the gasket(s) is (are) to be frequently replaced.
Such a known problem is particularly relevant in machines having important parts, such as for instance mechanical means for moving pistons, under the lower brewing piston.
The Applicant, in general, has noted that known brewing pistons do not effectively solve the problem of limiting or preventing leaks in a machine for infusion preparation, i.e. they do not solve the problem of impeding that some drop of water or coffee infusion powder pass through the piston gasket because of the gasket degradation.